The present invention relates to a fiber coupling lens that is applied to a photoelectric coupling module for efficiently collecting and focusing light from a semiconductor laser to be transmitted by optical fiber.
Optical communication is one of promising industries in recent years. In optical communication elements, a photoelectric coupling module includes a light source such as laser diode or LED, a fiber coupling lens and an optical fiber. A data light beam emitted from the laser diode passes the fiber coupling lens, then converges at the optical fiber for transmission. Refer to FIG. 1, due to small diameter of the optical fiber ranging from several microns to decades of microns and small size of the fiber coupling lens, not only precise alignment in directions (X-directions) perpendicular to the optical direction of the laser beam in the optical fiber is required, but also accurate alignment in the direction (Z-direction) of the optical axis is required.
Conventional fiber coupling lens may be formed by a single-piece of lens or multiple-piece lens. The fiber coupling lens formed by the multiple-piece lens collects maximum amount of light and has good focusing effect. However, single-piece type fiber coupling lens is more competitive in the market. As to short focal length (from a light source to focus point) single-piece type fiber coupling lens, a bi-convex design is the most common used, as shown in U.S. Pat. Nos. 5,764,838, 4,932,763, 5,293,269, and JP62059912. Generally, the diameter of the fiber coupling lens is quite small so that diffraction may happen when the distance to the focus point is relative long. Besides the problem of diffraction, alignment accuracy and coupling efficiency of the lens should also be required, as disclosed in U.S. Pat. No. 5,642,233, US2003/012496, JP09-061665, JP63-010119, JP05-273463, JP62-108217, JP02-150816, and JP07-128616 etc. Moreover, while the data light from a laser source of the photoelectric coupling module passing through the fiber coupling lens, the temperature of the lens will be increase. In order to avoid deformation of the fiber coupling lens caused by a long term heat exposure, the fiber coupling lens is made of glass by glass molding, as shown in JP63-297233, US2002/114085, TW240706, and TWD 076092 etc.
In order to achieve optimal effects of the fiber coupling unit (module), the fiber coupling lens has optical features such as small focal point, high coupling efficiency, and large numbers of apertures on objective side. In order to achieve above effects, conventional fiber coupling lens is designed to be formed by diffraction lens, as shown in WO2007145118, JP2006-227366, and US2003/0012496 etc. Yet such design also increases difficulties in manufacturing so that the cost is difficult to be reduced. Thus there is a need to develop a fiber coupling lens having simple optical surface with low cost and made by glass molding technique for enhancing development of optical communication industries.